1. Field of the Invention
The present invention relates to a gravity axis control method of a computerized numerically controlled machine tool, and more specifically, to a gravity axis brake control method of preventing an accidental detaching of a tool mounted on a gravity axis.
2. Description of the Related Art
In general, the Z axis of a vertical type machining center and the Y axis of a horizontal type machining center are referred to as a gravity axis and a tool mounted thereon becomes detached when a power supply is turned off or the excitation of a servo motor of the gravity axis is stopped. This unwanted detaching can be prevented by providing a mechanical brake which is actuated when the power supply is turned off. This brake is generally arranged to clamp the servomotor of the gravity axis when a current supplied to the brake is turned off.
In case of an emergency stop, a programmable controller (hereinafter, referred to as a PC) is notified that the control of the servo motor will be interrupted, whereupon the control of the servo motor is immediately interrupted and an exciting current supplied to the servo motor is turned off. At this time, the PC outputs a signal turning off the current to the brake, to cause the brake to lock the gravity axis.
Nevertheless, since the time at which a computerized numerical control (hereinafter referred to as CNC), interrupts the control of the servo motor and turns off the exciting current supplied to the servo motor of the gravity axis is not synchronized with the time at which the current supplied to the brake is turned off in response to the signal from the PC, thereby locking the gravity axis the tool on the gravity axis may be detached therefrom or the gravity axis may be subjected to shock.